GLAS cannot track taint through Class Level Variables (Java)

GLAS is unable to track tainted variables when assigned to class level variables:

public class Test extends HttpServlet {

    String userInput;
    String notUserInput = "REFRESH DB";

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        this.userInput = request.getParameter("input");

        // Rule works fine here
        vulnerableFunction(userInput);

        executeFunction1(userInput);

        executeFunction2();

        refreshDb();

    }

    private void executeFunction1(String userInput){

        //Rule works fine here
        vulnerableFunction(userInput);

    }

    private void executeFunction2(){

        //Rule fails to track taint in this scenario
        vulnerableFunction(userInput);

    }
}

Sample Playground link showing this behavior on the Semgrep Pro Engine: https://semgrep.dev/playground/s/Ped60

GitLab's GLAS Engine Exhibits the same behavior.

cc: @dabeles @mbenayoun @mtolpin @bhavyakaushal219-ext